Fix bug #3239 (Dragging a file onto Brackets to open it is broken on Win,
if you drag onto the editor area) - Revert 8f35d64's change enabling
CodeMirror dragDrop. This problem is the reason we had dragDrop disabled
in the first place.
Merge pull request #3242 from adobe/pflynn/fix-file-dragdrop

Fix bug #3239 (Dragging a file onto Brackets to open it is broken on Win)